To see someone "in person" means to see them directly, when you are both in the same place. When you know someone from seeing them on TV, talking to them on the telephone, etc., you get ideas about that person. After you meet them in person, you can compare the ideas you had about a person with reality with the phrases "more ___ in person" or "___er in person":
Bethany is a lot quieter in person than she is over the phone.
He's more intense in person than I imagined.